This invention relates to color imaging apparatuses, and more particularly to a color imaging apparatus which decomposes a single optical image into a plurality of optical images in primary colors and which picks up the respective images with corresponding image pickup tubes.
Heretofore, in the case of transmitting a picture of high quality as a video signal in a television broadcast service etc., there has been used a system wherein the optical image of an object is decomposed into primary colors and wherein image pickup tubes are disposed in correspondence with the optical images of the respective primary colors. For example, there has been used a three-tube type color imaging apparatus which is provided with three image pickup tubes corresponding to the three primary colors of red (hereinbelow, abbreviated to R), green (abbreviated to G) and blue (abbreviated to B). A four-tube type color imaging apparatus in which an imge pickup tube for obtaining a luminance signal is provided in addition to the three image pickup tubes for obtaining the signals of the primary colors R, G and B, and the like apparatuses have also been known.
As a technique common to these multi-tube type color imaging apparatuses, the so-called registration of images involving the placing of the pictures of the respective image pickup tubes one over another is required. In general, the multi-tube type apparatuses involve various distortions and positional deviations on account of lens aberration, the machining error of a lens-block color-separation system, the machining error of an electron gun in each image pickup tube, the error of a deflection coil assembly, etc. Usually, the distortions and the positional deviations include ones which are electrically corrected by changing the scanning position of an electron beam on the target plane of the image pickup tube, and ones which are corrected by changing the position of the image pickup tube by means of a mechanical adjusting mechanism provided for this purpose. In this regard, once the mechanical adjusting mechanism has been adjusted, it scarcely needs readjustments until the time of replacement of the image pickup tubes. In contrast, the troublesome operations of the electrical adjustments, specifically, the adjustments of the horizontal and vertical positions of the respective image pickup tubes, the adjustments of the horizontal and vertical amplitudes thereof, the adjustments of the horizontal and vertical linearities thereof, skew adjustments, the adjustments of pincushion distortions appearing at the corners of the respective pictures, etc. must be carried out each time the imaging apparatus is set up. Since the adjusting operations are also affected by a temperature rise within the imaging apparatus, they are ordinarily made after executing a heat run by closing a power supply 30 minutes to 1 hour before the use of the imaging apparatus. Accordingly, costs required for the adjustments (personnel expenditure, electric power, time loss) are huge.
In order to avoid such troublesome adjusting operations, there has recently been introduced an automatic setup system which employs a microcomputer.
A concrete example is "Automated Set-Up System For High Sensitive Handy Camera"
reported in IEE International Broadcasting Convention IBC 80, Conference Paper No. 191, pp.31-33.
With this imaging apparatus, a special pattern such as a wedge-shaped pattern for affording an adjusting criterion is contained in a taking lens for receiving the optical image of an object, and the misregistrations of the respective image pickup tubes are detected by utilizing the pattern. The adjustments of the registration are made with an auto-presetting registration system wherein the pattern in the taking lens is picked up by the respective image pickup tubes of R, G and B, the positional deviations involved are detected from the time deviations of the resulting output signals, a microcomputer is used to decide which directions the positional deviations may be corrected in, and adjusting circuitry is electrically and automatically controlled.
Although the introduction of the setup method has sharply shortened the setup time, deviations occurring during use after the presetting is completed cannot be corrected. More specifically, this system undergoes misregistrations during the use of the imaging apparatus or camera on account of disturbances after the presetting, specifically, the stability characteristic of each electronic circuit of the camera, the direction of geomagnetism, the change of the zooming ratio of a zoom lens, the mechanical expansion or contraction of an optical system-supporting portion ascribable to the generation of heat by the camera body, etc. In the future, the misregistrations will pose a problem especially in a color camera for a High Definition TV System (having, for example, 1,000-2,000 scanning lines).